Multistage heat exchanging duct comprising a parallel conduit

ABSTRACT

The heat exchanger having a heat exchanging channel ( 11, 21, 31 ) comprises an inlet ( 9 ) and an outlet ( 33 ) for a medium flowing through the heat exchanging channel. The heat exchanger has at least two stages ( 10, 20, 30 ) being arranged one after the other in view to the flowing direction of the medium, each stage having a heat exchanging channel ( 11, 21, 31 ). The first stage has at least one guiding channel ( 12 ) arranged parallel to the heat exchanging channel ( 11 ). The heat exchanging channel ( 11, 21, 31 ) has at the end of the respective stage ( 10, 20, 30 ) at least one outlet ( 13, 23, 33 ) and the guiding channel ( 12, 22 ) of the respective stage is connected with the heat exchanging channel ( 21, 31 ) of the next following stage ( 20, 30 ). By this unused heat transfer medium is fed to each stage, said heat transfer medium having a higher temperature difference with respect to the respective heat exchanging channel. By this a good heat transfer efficiency is realized even with relatively long flow pathes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from German application 10 2006 018709.1, filed Apr. 20, 2006, now Patent DE 10 2006 018 709; and fromGerman application DE 10 2006 035 552.0 filed Jul. 27, 2006, the entiredisclosures of which are incorporated by reference.

FIELD OF THE INVENTION

The invention relates to a heat exchanger of the type having an inletand an outlet and a channel through which a heat-exchanging mediumflows.

BACKGROUND OF THE INVENTION

Such a heat exchanger is for example known from DE 10 2004 030 675 A1.For cooling of electronic components, which are arranged within a switchcabinet, there is formed a channel together with a wall of the switchcabinet, and a medium such as air flows through the channel. The channelhas an inlet for cool air and an outlet for heated air. Cooling elementsare arranged on a channel wall, which shall provide for a better heattransfer from that wall to the air flowing along it.

Heat exchangers having successively arranged stages where each stage isfed with fresh medium are known from US 2004/0256092 A1 and US2002/0000311 A1.

Generally, the heat flow WF flowing along a surface A is proportional tothe temperature difference ΔT between the fluid and the surface A. As aproportiona-lity constant α the heat transfer coefficient in [W/m²*K] ischosen and therefore, it is valid:WF=α*A*ΔT  i.

The heat transfer coefficient α is dependent on material constants aswell as from the aforementioned cooling elements, which for exampleprovoke a turbulence.

From the above equation it can be seen that the cooling performance isproportional to the temperature difference ΔT. Where the flow path ofthe cooling fluid is longer, the cooling fluid is heated such that thetemperature difference along the flow path decreases and thereby thecooling performance decreases.

It is mentioned that analogous relationships are naturally valid for aheating, as for example a hot medium shall transmit heat to anotherobject, as for example to a plate. If in the following the words coolingor cooling efficiency are used, the same is also true in an analogousmanner for heating and heating efficiency.

As shown in the above mentioned prior art, it is often necessary to coolor heat elongated surfaces, wherein the problem of the decreasingcooling efficiency with increasing length arises.

A possibility for solving this problem is to increase the flow velocityof the fluid and therewith the flow rate of the fluid. This, however,requires greater dimensioned feeding devices for the fluid, thus forexample greater dimensioned blowers, which causes higher driving energyand therewith mostly a higher electrical current consumption as well asan increased required space and finally also a higher noise emission.

SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to improve the heatexchanger of the above-mentioned type in such a way that it has a goodperformance and simultaneously a small required space even with greatersurfaces to be cooled or to be heated.

This object is solved by the features mentioned in the claims.Advantageous embodiments and further developments of the invention areshown in the subclaims.

The basic principle of the invention lies therein to realize the heatexchanger from at least two or more successively arranged stages,wherein to each stage a “fresh” medium is fed, while the “used” mediumis discharged at the end of that stage.

Each stage, with the exception of the last stage, therefore has a heatexchanging channel and a guiding channel for “fresh” fluid, which withinthe respective stage does not take part on a heat exchange, wherein theheat exchange channel and the guiding channel are arranged parallel toeach other. At the end of each stage the fluid of the heat exchangechannel is discharged through outlet openings and “fresh” fluid of theguiding channel is fed to the heat exchanging channel of the next stageand, if required, to a further guiding channel of the next stage. Seenperpendicular to the flowing direction of the fluid, the fluid flows ofused and fresh fluid are crossing each other, wherein both flows areseparated from each other by guiding channels, which are denoted here as“cross flow elements”.

The individual stages may be designed modular such that theoretically asmany elements can be successively arranged after one another as desired.

Preferably, all heat exchanging channels of the individual stages arearranged within one plane, such that a simple geometrical structure isachieved, where the heat exchanging channel and the guiding channel eachhave the form of a cuboid. These channels also have a small flowresistance such that with a small dimensioned feeding device, as forexample blowers, considerable volume flows and therewith also heat flowscan be realised. According to a further development of the invention theoutlet of the heat exchanging channel of the respective stage isdesigned such that at least a guiding plate is deflecting the fluid in adirection to at least one sidewall of the heat guiding channel, whereinthe respective sidewall has an outlet opening there. Preferably, on bothsidewalls of the respective heat exchanging channels such outletopenings are present, wherein according to a preferred embodiment of theinvention the sum of the cross-sectional areas of the outlet openingscorrespond to the cross-sectional area of the heat exchanging channel.

The heat exchanger according to the invention has a small requiredspace, in particular because of its small height with respect to a planeperpendicular to the flow direction and therefore allows its use on bothsides of a surface, as for example a wall of a switch cabinet to becooled. Nonetheless, the heat exchanger according to the invention usesonly one fluid inlet. The incoming fluid is therewith divided withineach stage into at least two branch flows, which are fed to differentchannels.

A thermal interaction between the fluid and the surface occurs on theseparately ventilated areas of the surface within the heat exchangingchannel, wherein preferably measurement for improving the heat transferare used, as for example a rough surface, cooling ribs or micro ribsaccording to DE 102 33 736 B3 or similar.

The above mentioned cross flow elements do have the function to feed ordischarge the fluid to or from the respective surface areas of the heatexchanging channel and the guiding channel.

BRIEF DESCRIPTION OF THE FIGURES

In the following the invention will be described in connection with anembodiment in more detail by referring to the attached drawings. Itshows:

FIG. 1A schematic cross-section of a heat exchanger having three stagesaccording to an embodiment of the invention;

FIG. 2 A schematic top view of the heat exchanger of FIG. 1;

FIG. 3 A perspective view of the heat exchanger of FIGS. 1 and 2 seeninclined from above;

FIG. 4 A schematic side view of the heat exchanger similar to FIG. 1 butaccording to another variant of the invention;

FIG. 5 A perspective sectional view seen inclined from above of a heatexchanger according to a further embodiment of the invention;

FIG. 6 A perspective view seen inclined from below of the heat exchangerof FIG. 5; and

FIG. 7 A view of the lower side of the heat exchanger of FIGS. 5 and 6.

Same reference numbers of the individual figures refer to the same orfunctional related elements. Further, it is noted that the descriptionof a heat exchanger having three stages is not limiting. It is onlyrequired that at least two stages are present whereas no upperlimitation is given for a number of stages.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a schematic side view of the heat exchanger, which here hasthree stages 10, 20 and 30. The first stage 10 has a heat exchangingchannel 11, wherethrough a fluid, like for example air, may flow, namelywith a first part flow 14, which is denoted by an arrow. The heatexchanging channel 11 has a heat transfer wall 15, which is in a heattransferring interaction with the part flow 14, wherein this wall 15 maycomprise elements on its inner side, which improve a heat transfer, asfor example cooling ribs, roughnesses or micro ribs according to DE 10233 736 B3.

The heat exchange channel 11 further has a dividing wall 16, whichseparates the heat exchanging channel 11 from a guiding channel 12 lyingthereabove. The guiding channel 12 is closed by a topwall 18. Bothchannels 11 and 12 are closed at their sides by common side walls 19 and19 a (compare FIG. 2). Both channels have a common inlet 9 for a fluid,which is separated by the dividing wall 16 into part flows at the inlet9, namely a first part flow 14 flowing through the heat exchangingchannel 11 and at least an additional part flow 24 and/or 34 flowingthrough the guiding channel 12 and therewith is not in a heat exchanginginteraction with the heat exchanging channel 11 and the heat transferwall 15.

At the downstream end of the first stage 10 a “cross flow element” 8 isarranged, which on the one hand connects the heat exchanging channel 11with an outlet 13 by guiding plates; by the outlet 13 the first partflow 14 is discharged to atmosphere; on the other hand said cross flowelement 8 is connecting the guiding channel 12 with the second stage 20such that the part flows 24 and 34 are fed to the second stage 20. Thepart flows 14 on the one hand and 24 and 34 on the other hand areseparated from each other by the guiding plates and therefore are not ina heat transferring interaction with each other.

Because the first part flow 14 was in an heat exchanging interactionwithin the heat exchanging channel 11, its medium is “used” and has onlya small temperature difference ΔT with respect to the heat transfer wall15, whereas the part flows 24 and 34 comprise “unused” medium, whichstill has a relatively high temperature difference ΔT with respect tothe next following stages 20 and 30.

Referring to the view of FIG. 1 the first part flow 14 is discharged indirection to above via the opening of the outlet 13, whereas the partflows 24 and 34 are guided inclined to below, where they are dividedwithin the second stage 20 by the separating wall 26, which is providedthere. The second stage 20 has in an analogous manner a heat exchangingchannel 21 and a guiding channel 22. The part flow 24 flows through theheat exchanging channel 21 and is in a heat exchanging interaction witha wall 25, whereas the part flow 34 within the guiding channel 22 is notin any heat exchanging interaction with the wall 25.

In an analogous manner there is again a cross-flow element 7 at the endof the second stage 20, said cross-flow element 7 connects again viaguide plates the heat exchanging channel 21 with an opening 23 and theguiding channel 22 with a heat exchanging channel 31 of the third stage30, which here is the last stage and which therefore does not need aguiding channel but only a topwall 36 and here a heat exchanging wall35. At the outlet 33 of the third stage the used medium is dischargedwith a part flow 34.

In FIG. 2 each top wall 18, 28 and 36 is omitted in order to show atboth first stages 10 and 20 the inner part of the guiding channels 12and 22 and on the third stage 30 the inner part of the heat exchangingchannel 31. The cross-flow elements 7 and 8 are to be seen which in therespective upper plane of the guiding channels 12 and 22 do have guideplates 40, which are open into leadover channels 41; these leadoverchannels are inclined to below as seen in FIG. 1. In the transit areabetween the first stage 10 and the second stage 20 the separating wall26 is to be seen, where the part flows 24 and 34 are separated.

Further, guiding plates are depicted by dotted lines. It refers toguiding plates of the lowest plane of the respective heat exchangingchannels, which guide the fluid part flows into upwards directeddischarge channels 42 leading to the outlets 13 and 23 respectively.

FIG. 3 shows the heat exchangers in FIGS. 1 and 2 in a perspective viewseen inclined from above in a closed arrangement. The individualchannels described above are to be seen here in a good manner.

In FIG. 1 the heat transfer walls 15, 25 and 35 are depicted ascontinuously made of one part. However, it is also possible, as shown inFIG. 3, to design these walls individually so that the connectionbetween successively following stages is made only by the cross-flowelements 7 and 8.

In the embodiment of FIGS. 1 to 3 the heat exchanger has a single inlet9 for the fluid but three outlets 13, 23 and 33 for the part flows 14,24 and 34, said outlets being arranged one after another.

For some applications it is useful to have only one inlet and oneoutlet.

To this purpose the top wall 18 of the first stage 10 is elongated overthe whole heat exchanger of the variant of FIG. 4 such that for thesecond stage 20 above of its guiding channel 22 still an additionalguiding channel 44 is provided, within which the part flow 14 isdischarged and at the end of the second stage is joined with the partflow 24 such that overall only one outlet 33 is provided. It is evidentthat the outlets 13 and 23 of the embodiment of FIG. 1 lead into theguiding channel 44 in this embodiment.

The heat exchanger of the invention is mounted by a small number ofsimple basic elements, which can be combined in a manner of a kit inorder to adapt the capacity of the heat efficiency to the individualapplication. The individual stages and the downstream cross-flowelements may be designed as a module, wherein modules for the first,second, third, fourth etc. stages are manufactured, which preferably maybe coupled by a plug connection, wherein only the individual stages areto be plugged together and in some applications are connectedadditionally by for example adhesive bonding, soldering, welding orother known methods for connection. The individual basic elements arecomprised by thin plates, which may be made of metal or plastics andwhich can be plugged into each other and/or which can be glued with eachother. The heat exchanger therefore has a small weight and can beconnected to a surface to be cooled or to be heated without substantialeffort.

Generally, it is possible to omit the heat transfer wall 15, 25 and 35and therefore a surface of an object to be cooled or to be heated formsthe lower side of the individual heat exchanging channel. It is to beunderstood that the heat transfer walls 15, 25 and 35 are to be madefrom material which has good heat conducting properties.

According to the invention the individual stages 10, and 30 may be bentin order to adapt it to the contour of the object to be cooled or to beheated.

The FIGS. 5-7 show a second embodiment.

FIG. 5 shows an object 1 to be cooled or to be heated having a flatsurface whereon the heat exchanger 3 is placed. The heat exchanger 3 hashere again three stages 10, 20 and 30, which are arranged after eachother in flowing direction of a heat transferring medium, as for exampleair. Each of the three stages 10, 20 and 30 has a heat exchangingchannel 11, 21 and 31, respectively, which is limited here on the onehand by a planar surface 2 of the object 1, by sidewalls 4 and 5 (FIGS.6 and 7) and a limiting wall 16, 26 and 36, wherein the limiting wall 36of the last stage 30 has the function of a top wall.

The heat exchanger 3 is designed such that the medium fed to theindividual stages 10, 20 and 30 and therewith to the individual heatexchanging channels 11, 21 and 31 is “fresh” medium and not a “used”medium, wherein the fresh medium has not taken part to a heat exchangingaction within a preceding stage before reaching the respective heatexchanging channel.

The heat exchanger 3 has a common inlet 9 for the medium, which is heredivided within the shown three staged heat exchanger into three partflows 14, 24 and 34, by arranging parallel to the limiting wall 16 ofthe first heat exchanging channel 11 two additional walls 17 and 18,which form together with the sidewalls 4 and 5 guiding channels 12 and13 for the part flows 24 and 34, wherethrough the medium flows withouttaking part on the heat exchanging action of the first heat exchangingchannel 11.

As best can be seen in FIG. 7, a guiding plate 40 is arranged within thefirst heat exchanging channel 11, said guiding plate 40 limits therearmost side of the heat exchanging channel 11, with respect to theflow direction, by two curved brackets and guides the part flow 14 toopenings 13 within the side walls 4 and 5.

By this, at the downstream end of the first exchanging channel the usedmedium then is discharged laterally, wherein the flow can be deflectedto above, i.e. perpendicular to the planar surface 2, by chimney likelateral projections 13′, or also inclined to above. The cross-sectionarea of both lateral openings 13 correspond essentially to thecross-section area of the heat exchanging channel 11, such that themedium with the part flow 14 (FIG. 7) can be discharged essentiallyfreely and therefore the flow resistance is very small.

The guiding channel 12 of the first stage is connected with the heatexchanging channel 21 of the second stage because the upper wall 17 ofthe guiding channel 12 is connected via an inclined wall 46 with thelimiting wall 26 of the second heat exchanging channel 21. Therewithfresh medium flows with the part flow 24 into the second stage 20 andtakes part in heat exchanging action. The second stage 20 is completedin the same manner by an identical guiding plate 29, which leads tolateral openings 23 in the walls 4 and 5, such that at the downstreamend of the second stage the part flow 24 can be discharged through theseopenings 23, wherein also here the sum of the cross-section areas of theopenings 25 corresponds to the cross-section area of the second heatexchanging channel 21.

Above of the second heat exchanging channel 21 again a guiding channel22 is provided, which is formed between the limiting wall 26 and the topwall 27, which runs parallel to the limiting wall 26. The top wall 27 isconnected with the wall 18 via an inclined running wall 43, such thatthe part flow 34 from the first stage 10 and its guiding channel 13flows into the guiding channel 23 of the second stage 20 and therefromagain via an inclined running wall 47 into the third stage 30, which isformed by the top wall 36 and both sidewalls 4 and 5. At the end of thethird stage 30 no guiding plates analogous to the guiding plates 40 and29 are provided. Instead, the medium flows with the part flow 34 at thedownstream end of the third heat exchanging channel 31 through anopening 31. If it is desired to have the discharged air generally in thesame direction, it is also possible to provide there in an analogousmanner a guiding plate as well as lateral openings analogous to theopenings 15 and 25.

FIG. 5 still shows that in the transfer area from the preceding guidingchannel to the respective heat exchanging channel 21 or 31 additionalguiding plates 41 and 48 may be provided, which run parallel to theinclined running plates 43, 46 and 47. By this a uniform flow is reachedand turbulences on the downstream side of the guiding plates 40 and 29are avoided. It is noted that these plates 41 and 48 may be omitted andtherefore, the respective medium can reach downstream of the guidingplates 40, 29 the heat guiding channel of the next stage. The top walls16 and 26 then end downstream at the guiding plates 40 and 29.

As best can be seen in FIG. 7 the part flows 14 and 24 of used mediumcan be discharged at the downstream end of the individual heatexchanging channel either laterally through the walls 4 and 5 parallelto the surface 2 (FIG. 5) of the object to be cooled as shown at theopenings 23 in FIG. 7, or they can be deflected by guiding chimnies 13′,which are mounted laterally to the openings 13 so that the medium isdischarged vertically with respect to the surface 2.

Further, it is noted that the form of the guiding plates 40 and 29 canbe modified. The preferred variant is the form of an arc of a circle,which best can be seen in FIG. 7 having two arcs of a circle which formin the middle of each respective heat guiding channel an apex dividingthe flow. It is also possible to use straight or V-like guiding channelswhich are arranged symmetrically or asymmetrically. If for certainapplications a discharging of used medium is wanted only to one side itis also possible to provide for only one lateral opening in one of bothsidewalls 4 and 5, wherein then the respective guiding plate runsinclined through the whole heat exchanging channel. Further, in FIG. 7 avariant is shown where the inclined plate 48 of FIG. 5 is omitted suchthat the medium flows from the guiding channel 23 on the downstream sideof the guiding plate 29 directly into the third heat exchanging channel.

The embodiment of FIG. 6 shows in a perspective view seen inclined frombelow the heat exchanger according to the invention, wherein here bothlateral openings 13 and 23 are connected to chimney-like projections 13′and 23′.

The invention claimed is:
 1. A heat exchanger comprising: a heatexchanging channel having an inlet and an outlet for a medium flowingthrough the heat exchanging channel, at least two stages being at leasta first stage and a second stage of the heat exchanger arrangedsequentially in a flow direction of the medium, each stage having a heatexchanging channel segment such that there is a first heat exchangingchannel segment and a second heat exchanging channel segment, whereinthe first stage comprises at least one guiding channel closed by a topwall and arranged parallel to the heat exchanging channel segment of thefirst stage and wherein flow paths of the at least one guiding channeland of the heat exchanging channel segment in the first stage are inseparate planes, wherein each heat exchanging channel segment has atleast one outlet at the end of the respective stage, and wherein theguiding channel of the first stage is in flow connection with the heatexchanging channel segment of the second stage, wherein each of thefirst and second heat exchanging channel segments has at its downstreamend a guiding plate for discharging the medium through an opening oropenings, which is/are provided within a side wall of the respectiveheat exchanging channel segment and wherein this discharge is laterallyof the heat exchanging channels at the downstream end of the first heatexchanging channel segment and at the downstream end of the second heatexchanging channel segment.
 2. The heat exchanger according to claim 1wherein the stages are connected with each other by plug connections. 3.The heat exchanger according to claim 2 wherein each heat exchangingchannel segment has at least one guiding channel and wherein the heatexchanging channel segments and the guiding channels are designed in theform of a cuboid.
 4. The heat exchanger according to claim 3 wherein theheat exchanger comprises more than two stages.
 5. The heat exchangeraccording to claim 4 wherein the guiding channels of all stages prior tothe last stage are in flow connection with the heat exchanging channelsegment of a next stage.
 6. The heat exchanger according to claim 4wherein the heat exchanger comprises a top wall covering all stages,wherein said top wall forms an additional guiding channel, and whereinthe outlets of each stages with the exception of the last stage run intosaid guiding channel formed by the top wall.
 7. The heat exchangeraccording to claim 2 wherein the heat exchanger comprises more than twostages.
 8. The heat exchanger according to claim 7 wherein the guidingchannels of all stages prior to the last stage are in flow connectionwith the heat exchanging channel segment of a next stage.
 9. The heatexchanger according to claim 1 wherein each heat exchanging channelsegment has at least one guiding channel and wherein the heat exchangingchannel segments and the guiding channels are designed in the form of acuboid.
 10. The heat exchanger according to claim 1 wherein theindividual stages are glued with each other.
 11. The heat exchangeraccording to claim 1 wherein the heat exchanger is manufactured fromplastics or metal.
 12. The heat exchanger according to claim 1 whereinthe heat exchanger comprises more than two stages.
 13. The heatexchanger according to claim 12 wherein the guiding channels of allstages prior to the last stage are in flow connection with the heatexchanging channel segment of a next stage.
 14. The heat exchangeraccording to claim 12 wherein the individual stages are designed in amodular manner.
 15. The heat exchanger according to claim 1 wherein theheat exchanger comprises said top wall and said top wall covers allstages, wherein said top wall forms an additional guiding channel, andwherein the outlets of each stages with the exception of the last stagerun into said guiding channel formed by the top wall.
 16. The heatexchanger according to claim 1 wherein a cross-sectional area of theopening or the openings corresponds with the cross-section area of therespective heat exchanging channel segment.
 17. The heat exchangeraccording to claim 1 wherein the guiding plate comprises two brackets,which are connected to each other in an acute manner.
 18. The heatexchanger according to claim 17 wherein the brackets of the guidingplates are bent in a curved manner.
 19. The heat exchanger according toclaim 1 wherein the guiding plate is arranged in a top viewmirror-symmetrically to the middle of the heat exchanging channelsegment.
 20. The heat exchanger according to claim 1 wherein achimney-like projection is connected to the opening, which projection isarranged to deflect the medium discharged from the opening in such a waythat it has at least a medium flowing component vertically to the mainflowing direction through the heat exchanger and vertically to the exitdirection from the opening.
 21. The heat exchanger of claim 1 whereineach stage is connected to an adjacent stage by a cross-flow element insuch manner to yield separated part flows of the medium and thecross-flow element is arranged to direct medium from the heat exchangingchannel segment of the first stage toward an outlet.
 22. The heatexchanger of claim 1 wherein each stage is connected to an adjacentstage by a cross-flow element in such manner to yield separated partflows of the medium and the cross-flow element is arranged to directmedium from the at least one guiding channel of the first stage to theheat exchanging channel segment of the second stage.
 23. The heatexchanger of claim 1 wherein each stage is connected to an adjacentstage by a cross-flow element in such manner to yield separated partflows of the medium and the cross-flow element is arranged to directmedium from the heat exchanging channel segment of the first stagetoward an outlet, and to direct medium from the at least one guidingchannel of the first stage to the heat exchanging channel segment of thesecond stage.
 24. The heat exchanger of claim 1 wherein each stage isconnected to an adjacent stage by a cross-flow element in such manner toyield separated part flows of the medium and the cross-flow elementcomprises an outlet and is arranged to direct medium from the heatexchanging channel segment of the first stage through the outlet, and todirect medium from the at least one guiding channel of the first stageto the heat exchanging channel segment of the second stage.
 25. The heatexchanger of claim 1 wherein each stage is connected to an adjacentstage by a cross-flow element in such manner to yield separated partflows of the medium and the cross-flow element is arranged to directmedium from the heat exchanging channel segment of the first stage awayfrom a transfer wall plane of the exchanger, and to direct medium fromthe at least one guiding channel of the first stage toward the transferwall plane of the exchanger and to the heat exchanging channel segmentof the second stage.